A variety of electronic devices have various structures in their inputting sections. Portable devices, among other electronic devices and typically represented by portable phones, have increasingly used a panel switch as an operating panel. The panel switch is formed by placing a movable-contact unit on a printed wired board of an electronic device, and the movable-contact unit is formed by adhesively holding movable contacts on the underside of a base sheet made of insulating film such as PET.
Due to their portability, the portable devices can be used in various environments including a wide range of temperature, so that the operating panel needs to be capable of operating smoothly in the various environments. The foregoing conventional movable-contact unit and the panel switch using the conventional movable-contact unit are described hereinafter.
FIG. 6 shows a sectional view of the conventional movable-contact unit, FIG. 7 shows a sectional view of the panel switch formed of the conventional movable-contact unit, and FIG. 8 shows a perspective exploded view of the same panel switch.
As illustrated in the sectional view of FIG. 6, conventional movable-contact unit 10 is formed this way: domed movable contact 5 made of a thin metal sheet is held on the underside of base sheet 1 at its center top face, which base sheet 1 is made of insulating film such as PET. In general, adhesive 3 is patterned on the underside of base sheet 1, and then movable contact 5 is adhesively held by holding section 3A of adhesive 3.
The placement of movable contacts 5 is determined in response to an operating panel of a device, and a plurality of movable contacts 5 are placed independent of each other, thereby forming panel switch 20.
Adhesive 3 formed on the underside of base sheet 1 is also available around movable contacts 5, and the surrounding sections 3B of adhesive 3 holds separator 7, which has a top face that has undergone a releasing process, on the underside of sheet 1. Separator 7 is laminated entirely on the underside of sheet 1 in order to prevent the adhesion of dust to movable contacts 5 during transportation and storage.
Before movable-contact unit 10 is used, separator 7 is removed by using its releasing process, and movable-contact unit 10 is bonded to wired board 15 (ref. FIGS. 7 and 8) of the device by surrounding sections 3B exposed at the underside of base sheet 1. Wired board 15 includes a fixed contact on its top face, and the fixed contact is formed of outer fixed contact 17A and center fixed contact 17B in pairs.
As shown in FIG. 7, each one of contacts 5 of movable-contact unit 10 is placed on outer fixed contact 17A corresponding to the contact 5 at its lower end of the outer rim, so that contact 5 is adhesively placed on wired board 15, thereby forming panel switch 20. On top of panel switch 20, key mat 25 is placed for depressing movable contact 5, so that the operating panel is constructed.
Panel switch 20 operates this way: key mat 25 is depressed at its keytop, such that pressing force is applied to corresponding movable contact 5 via base sheet 1. When the force exceeds a given value, the center of movable contact 5 is reversed producing tactile feedback, so that the bottom of contact 5 touches center fixed contact 17B, i.e. outer fixed contact 17A is shorted to center fixed contact 17B via movable contact 5. When the depressing force is removed, movable contact 5 restores itself to its original position (switch-off position as shown in FIG. 7).
Panel switch 20 discussed above provides the user with excellent tactile feedback (click feeling) in a slim structure, so that it has been widely used in portable phones which have become progressively slimmer.
It has recently been preferred to have the keytop of key-mat 25 illuminated, and thus it has been proposed that an LED mounted on wired board 15 as a light source for the illumination be replaced with an EL (electro luminescent) sheet. Because the EL sheet can be used as a surface light source and allows illumination of an object with its surface emission. FIG. 9 shows a sectional view of an example of the EL sheet, and this example, called an inorganic EL sheet, comprises the following elements:
(a) optically transparent base film 30 made of, e.g. PET (polyethylene terephthalate), and placed on the light emitting side, i.e. placed as the top face of the EL sheet; and
(b) transparent electrode layer 31, light emitting layer 32, dielectric layer 33, back electrode layer 34, and insulating layer 35, laminated and printed on the underside of film 30 in this order. It has been proposed that this inorganic EL sheet 40 be placed beneath key mat 25, or that movable contacts 5 be bonded directly to EL sheet 40, thereby forming a movable-contact unit. Related prior art is disclosed in, e.g. Unexamined Japanese Patent Publication No. H10-144172, or No. 2001-273831.
Recently, devices have been downsized and slimmed, so that the inventors of the present invention think that a surface light source in a slim body is useful as a movable-contact unit, one of the elements of an operating panel of the devices. The inventors thus have studied the replacement of base sheet 1 of conventional movable-contact unit 10 with inorganic EL sheet 40.
The movable-contact unit under study employs inorganic EL sheet 40; however, EL sheet 40 has a problem in that it is thicker than conventional base sheet 1 because of its multi-layer printings, and yet, it becomes highly rigid in a low temperature environment. The inventors thus encountered the problem that the operation in the low temperature environment provides the user with degraded tactile feedback obtained from movable contacts 5. In the environment at −20° C. that is generally the lower limit of operating a mobile communication device such as a portable device, almost no tactile feedback is obtained from movable contacts 5.